Be careful with typography.
All the characters of the same typeface are not the same height.
The "O,S,G" mainly rounded letters are always higher than the others,
to visually compensate for the extra void they leave beside them.
If these were of the exact same height as the rest of the alphabet, they would appear smaller and out of place. Try it, you'll see.
So, careful when dimensioning letters individually.
I always take my dimensions from a square letter such as M or T and let the rest flow.